11.2020 | THE SCIENTIST 31BARBIE HALASKA, THE MARINE MAMMAL CENTER
Act, the population rebounded so well
that gray whales were removed from the
endangered species list in 1994. Then
came the exceptional number of dead
whales washing ashore.
The similar pattern now unfolding,
with an uptick in deaths following a pop-
ulation boom, fingers carrying capacity as
a prime suspect. But, Calambokidis notes,
it’s too soon to close the case on the recent
gray whale deaths. That’s because the car-
rying capacity argument doesn’t address
some key unknowns about the food sup-
ply, such as whether the whales’ diet is
changing due to “the dramatic changes
that are occurring in the Arctic environ-
ment,” he says.
Moore agrees that warming temper-
atures and melting sea ice in the Arc-
tic have to be considered. “The reason
I have a little problem with [the argu-
ment that] all these whales are starving
because they’ve hit this hard carrying
capacity,” she says, “is that gray whales
are very adept at eating a lot of different
things.” They particularly like to chow
down on amphipods during the sum-
mer months in the Arctic, and also eat
krill and other small crustaceans as wellas herring roe while migrating along the
North American coast.Arctic warming as a possible killer
For more clues to what’s killing gray
whales, researchers are slicing deeper
into the animals that have washed
ashore. If a beached whale has been dead
for a day or less, scientists can cut into
the animal’s skin and blubber to mea-
sure the thickness of the fatty layer and
take samples to analyze its lipid levels.
“How thick the blubber is and, more
importantly... the level of oil and lipids
in the blubber and some internal body
cavities tell you about the health of the
animal,” Calambokidis says.
While the blubber thickness has
been seemingly similar across the years,
whales that have washed ashore recently
have less oily blubber and more watery
blubber compared with whales autopsied
prior to 2019, he says. “We’ ve had cases
where the blubber layer is still thick,
but we’ll cut, and we can see it’s dry and
fibrousy.” He says it’s “like all the oil and
material has been... sucked out of it.”
In nine emaciated whales studied last
year, the researchers also noticed that theanimals’ blubber was discolored, appear-
ing as a washed-out pink rather than the
more rosy color of healthy blubber. An
analysis of the discolored blubber under
the microscope revealed a disproportion-
ate increase in collagen fibers relative to
fat cells, along with structural changes
to some of the fat cells themselves. The
results suggested that the whales weren’t
getting the nutrition needed to maintain
healthy blubber, leading some research-
ers to suspect that the marine mammals’
diet could be changing, becoming less
nutritious. “Polar seas are warming twice
as fast as in other places, and we know
that that is changing aspects of the eco-
system,” says Moore.
Gray whales dine on small, shrimp-
like crustaceans called amphipods
that they siphon off the bottom of theRecently stranded whales
have less oily blubber
and more watery blubber
compared with whales
autopsied prior to 2019.BEACHED: An adult female gray whale measuring more than
12 meters long washed up at California’s Point Reyes National
Seashore in April 2019.